As example, I want make simple resizer, where you can select image in explorer and set new dimensions.
It is not possible to modify the Windows Explorer 8 ribbon.
However, add-ins will not be able to plug into the ribbon UI. This was a difficult engineering choice for us and we expect that many of you will read this and suggest we add the capability--of course if we could get it right this time around we would have done that. A big part of this blog is sharing these choices--tradeoffs--between new features and adding everything we can dream up and finishing. We also think the customization we provide and the improvements are worthwhile this time around.
From here.
来源：https://stackoverflow.com/questions/10580362/how-extend-windows-8-explorer-ribbon-with-custom-controls